The notes, which retain the image of American statesman andscientist Benjamin Franklin, include two new security features -a blue three-dimensional security ribbon with images of bellsand 100s, and a color-changing bell in an inkwell, the Fed saidin a statement.

The $100 bills, the biggest U.S. denomination known inAmerican slang as "Benjamins," also keep security features fromthe previous design, such as a watermark.

"The new design incorporates security features that make iteasier to authenticate, but harder to replicate," said FederalReserve Board Governor Jerome Powell said in a statement.

U.S. officials have said the $100 note is the mostfrequently counterfeited denomination of U.S. currency outsidethe United States due to its broad circulation overseas. In theUnited States, the $20 bill is the most frequently counterfeitednote.

Sonja Danburg, program manager for U.S. currency educationat the Fed, said about 3.5 billion new $100 bills had beenstockpiled. There are about $900 billion in $100 notes incirculation, with half to two-thirds outside the United States,she said.

The United States has about $1.15 trillion in genuine currency in circulation, and less than 1/100th of 1 percent ofthat value is counterfeit, Danburg said.

Benjamins are the highest-denominated notes issued by theFederal Reserve since the United States stopped issuing $500,$1,000 and $10,000 notes in 1969.

The new bills have been in development since 2003. The newbills cost about 12.5 cents each to make, 5 cents more than theprevious notes because of the greater complexity of the design,Danburg said.

The average $100 bill lasts about 15 years before wearingout and being pulled from circulation. The more frequentlyhandled $1 note lasts about six years, Danburg said.

The Fed said people with old bills did not need to tradethem in for new ones since all designs of U.S. currency remainedlegal tender.